Felicity Huffman has been charged as part of a multi-million dollar college cheating scandal.

Felicity Huffman and Full House star Lori Loughlin are among dozens of people arrested for a $US25 million ($A35 million) scheme to help wealthy Americans cheat their children’s way into elite universities, such as Yale and Stanford.

The largest college admissions fraud scam unearthed in US history was run out of a small college preparation company in Newport Beach, California, that relied on bribes, phoney test takers and even doctored photos depicting non-athletic applicants as elite competitors to land college slots for the offspring of rich parents, prosecutors said.

Huffman, of Desperate Housewives fame, and her husband, Shameless actor William H. Macy, allegedly paid US$15,000 so their daughter could double the time to complete her university entrance exam.

However, when it came time for her second daughter to finish high school, the Desperate Housewives actress allegedly opted not to hire the same services.

“Ruh Ro! Looks like [my daughter’s high school] wants to provide own proctor.” — Felicity Huffman, allegedly. pic.twitter.com/QL4tNmvW1l

— Ryan J. Reilly (@ryanjreilly) March 12, 2019

Loughlin, meanwhile, allegedly “agreed to pay bribes totalling $500,000 in exchange for having their two daughters designated as recruits to the USC crew team,” according to legal documents.

That’s despite Loughlin and her husband Mossimo Giannulli’s daughters, Isabella Rose and Olivia Jade Giannulli, not actually being gifted in rowing.

Huffman and Loughlin were due to appear in federal court in Los Angeles later on Tuesday (Wednesday, Australian time), prosecutors said.

Andrew Lelling, the US attorney in Boston, said at a news conference on Tuesday that the dozens of parents “are a catalogue of wealth and privilege”.

“For every student admitted through fraud, an honest, genuinely talented student was rejected.”

Federal prosecutors in Boston charged William "Rick" Singer, 58, with running the scheme through his Edge College & Career Network, which charged from $US100,000 to as much as $US2.5 million per child for the services, which were masked as contributions to a scam charity Singer runs.

About 300 law enforcement agents swept across the country on Tuesday to make arrests in what agents code-named "Operation Varsity Blues".

Prosecutors have named 33 parents, 13 coaches, and associates of Singer's business, but said the investigation continues and more parents and coaches could be charged.

Singer is scheduled to plead guilty on Tuesday in Boston federal court to charges including racketeering, money laundering and obstruction of justice, according to court papers. He could not be reached for immediate comment.

The alleged masterminds of scam and parents who paid into it could all face up to 20 years in prison if convicted.

Prosecutors said it was up to the universities what to do with students admitted through cheating.

Yale University and the University of Southern California said in separate statements that they were co-operating with investigators.

Prosecutors said the scheme began in 2011 and also helped children get into the University of Texas, Georgetown University, Wake Forest University and the University of California, Los Angeles.

Part of the scheme involved advising parents to lie to test administrators that their child had learning disabilities that allowed them extra exam time.

The parents were then advised to choose one of two test centres that Singer's company said it had control over: one in Houston, Texas, and the other in West Hollywood, California.

The test administrators in the those centres took bribes of tens of thousands of dollars to allow Singer's clients cheat, often by arranging to have wrong answers corrected or having another person take the exam. Singer would agree with parents beforehand roughly what score they wanted the child to get.

In many cases, the students were not aware that their parents had arranged for the cheating, prosecutors said, although in other cases they knowingly took part. None of the children were charged on Tuesday.

Singer also helped parents stage photographs of their children playing sports or even Photoshopped children's faces on to images of athletes downloaded from the internet to exaggerate their athletic credentials.